Originally Posted by surlynkid
do not double up the o-ring. it will really leak then. you can easily remove the o-ring, measure it, and then buy one that is thicker. that can be tricky though as what i think you want is more depth while maintaining ID and OD to fit. whatever you buy, make sure it is of the right material and durometer to withstand the duty. sounds like you want a custom fit gasket which any o-ring and gasket shop can make. just give them the dimensions and material specs.
Unfortunately, depending on where you live, a "o-ring and gasket shop" is kinda hard to come by.
If someone could source these, I think it's something a lot of us would want.